This invention relates to a method and apparatus for the control of fuel consumption in an airplane.
It is well known that during the cruise flight for every altitude and for every airplane gross weight there is an optimal air speed at which the greatest fuel economy can be obtained. The efficiency of the fuel consumption can be evaluated by the criterion "specific range", calculated as a ratio of the "ground speed" and the "fuel flow rate", measured in distance perunit of fuel (e.g. km/ton). The relationship between the specific range and air speed (or Mach number) is represented by a smooth curve with a single maximum of the specific range at a certain value of the air speed. So, it is possiblbe to fly at maximum specific range, adjusting the air speed at the appropriate optimal value, via corresponding setting of the thrust of the airplane. This can be done manually by the pilot if there is a calculating unit, or by an automatic system, incorporating some methods of search and control.
The main disturbance causing a shift of the specific range maximum to the direction of lower air speeds is the continuous decrease of the airplane's weight, due to the fuel consumption. This one, and some other disturbances, as varitions of wind direction and velocity, of air temperature, change of cruise altitude, etc., make it necessary to search periodically, or better continuously, a new maximum.
A known method for the control of fuel consumption of different types of airplanes consists in the following steps: at the beginning of the cruise flight the maximum value of the specific range is to be found via manual adjustment of the engines' throttles. After fining the maximum the pilot has to maintain the air speed constant for a pre-determined tim etinerval, and then a new maximum of the specific range is to be searched. These two steps are repeated during the hwole cruise flight. (See, for example, fuel Management Computer Model CD-3000, Airlines Pilots Operating and Reference Manual, 1981, Aero Systems Inc.)
A drawback of the above-described known method is that the maintenance of a constant air speed in the intervals between two subsequent searches of the maximum specific range results in a shift away from the optimum conditions because of the reduction of the weight of the airplane due to the consumption of fuel. Moreover, the variations of the external conditions, such as altitude, wind and air temperature, result in an additional change of the position of th maximum of the specific range and corresponding optimal air speed. Until the elapse of the time between two searches, the shift of the maximum remains uncontrollable and the airplane flies a long time at non-optimum air speed and fuel consumption. Moreover, during the process of search of the maximum specific range the method does not provide the necessary information for the direction of search, i.e. increasing or decreasing the thrust, the magnitude of the thrust increments and for the moment when the search must stop. This results in an increase of the number of search steps and to an additional excessive consumption of fuel.
The aforedescribed method for the control of fuel consumption is effected by a system comprising transducers for detecting ground speed and fuel flow rate, connected to a computing microprocessor, which is connected via an output interface to a digital indicator and a keyboard (See, Management Computer model CD-3000, supra). The drawbacks of the known method are inherent in the known apparatus as well.
It is, therefore, a general object of this invention to provide a method and an apparatus for the control of fuel consumption which is featured by an increased degree of control efficiency.